August 1895.] 



PSrCHE. 



271 



HABITS AND PARASITES OF STIGMUS INORDIXATUS FOX. 



BV A. IIAVIDSOX, M. D., LOS ANGELES, CAL. 



Judging from the lumiber of tun- 

 nels excavated by this species in soft 

 stemmed plants and friable rock, it must 

 be somewhat common in this vicinity, 

 although on account of the small size 

 and rapid flight it is very seldom seen. 

 The only time I have ever seen it flying 

 was when watching near their excava- 

 tions, at wliicb time the wasp with its 

 prey may be easily captured. They 

 usually buikl their cells in tunnels ex- 

 cavated in the stems of the l)ramble, 

 black mustard, dock, or other pithy 

 plants; but not infrecjuently they may 

 be found in binrows in tlie soft sand- 

 stone abounding in this district. The 

 plant-stems invariably chosen for a nest- 

 ing site are those already severed, or 

 broken sufiiciently to expose the pith. 

 In the center of this a tunnel of varying 

 depth is excavated. I have a specimen 

 in my possession in which tliis tiny 

 insect has formed a tunnel 12 inches 

 deep and built and provisioned therein 

 30 cells. The latter measure on an 

 average one-fourth inch in length by 

 one-sixteenth in witlth ; but both are 

 variable, the width frequently being 

 one-eighth of an inch. This wasp stores 

 its nest with the common aphis, 20 of 

 which arc on an average requiied to 

 provision each crlL The partitions 

 between the cells are composed of pith 

 and var)' in thickness. From speci- 

 mens wliich I secured in the autumn 



the mature insects issued in February 

 and Marcli, but the discovery of freshly- 

 made cells in February and throughout 

 the smiimer gives me the impression 

 that while the majority of the adults 

 issue in the spring, j-et they are more 

 or less active all the year round, in 

 which respect they are unique among 

 the native hymenoptera of m}' acquain- 

 tance. The larvae spin no cocoons the 

 light yellow pupa lying on its back in 

 the cell. Of the parasites, but two 

 species have been bred thus far; viz.: 

 Omahis iridesceiis Nort., and a new 

 species of Eiuytoma. Of the former 

 only two specimens were reared, from 

 separate cells ; both had pupated when 

 discovered in February, and hatched 

 out March 14. Of the Eurytoma, of 

 which a description has been kindly 

 furnished by Mr. Ashmead, a dozen 

 specimens were bred. Each occupied 

 a separate cell which showed no trace 

 of wasp remains; they spmi no co- 

 coons, and were about two weeks later 

 in hatching out than the wasps in the 

 .same burrows. 



Mr. Ashmead's description of the 

 new Eurytoma is as follows : — 



Enrvtonia .•iO'^rfit A^\]ui, n. sp. 



$. Length 3111111. Black, uinbilicately 

 punctate, clothed with sparse white pile; an- 

 tennae entirely black; apical half of anterior 

 femora, their tibiae, except a black .stripe 

 outwardly, and .all their tarsi, except the last 



